Front Cover. Acid-mine drainage found below the Duke mine, a massive sulfide

deposit in the Prince William Sound area, Alaska (lower left); collecting water samples

downstream from the Drenchwater massive sulfide deposit in the northwestern Brooks

Range, Alaska (upper right).

Right. A sample of the ore mineral cinnabar (red mineral) collected from one of

several abandoned mercury mines in southwestern Alaska. The mines in the

region were studied to evaluate effects of mercury on surrounding ecosystems.

Above. Geologists from the U.S. Geological Survey collecting water samples

downstream from a massive sulfide deposit, northwestern Brooks Range, Alaska.

Stream characteristics such as trace-element concentrations in stream sediments

and stream waters, and streamwater pH and conductivity were measured

downstream from several mineral deposits in Alaska to evaluate effects of these

deposits on surrounding environments.
Environmental Studies of

Mineral Deposits in Alaska

U.S. GEOLOGICAL SURVEY BULLETIN 2156

Short articles summarize environmental geochemical studies of metallic

mineral deposits in Alaska, including massive sulfide, gold, mercury,

chromium, and uranium mines and deposits. The studies report metal and acid

concentrations in samples collected around such mines and deposits, and

evaluate environmental effects of the deposits. The articles are written in a style

intended to reach a general audience

Edited by John E. Gray and Richard F. Sanzolone

With contributions from

Elizabeth A. Bailey Karen D. Kelley Richard F. Sanzolone

Helen W. Folger Keith A. Mueller* Elaine Snyder-Conn*

Richard J. Goldfarb Steven W. Nelson Clifford D. Taylor

Larry P. Gough James K. Otton Peter M. Theodorakos

John E. Gray John A. Philpotts

*U.S. Fish and Wildlife Service

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1996

M A R C H 3, 18 4 9

U.S. DEPARTMENT OF THE INTERIOR
For sale by U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and

does not imply endorsement by the U.S. Government

Library of Congress Cataloging-in-Publication Data

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

Environmental studies of mineral deposits in Alaska / edited by John E. Gray and Richard 

F. Sanzolone ; with contributions from Elizabeth A. Bailey . . . . [et al.].

p. cm.—(U.S. Geological Survey bulletin ; 2156)

Includes bibliographical references (p. ).

1. Metals—Environmental aspects—Alaska. 2. Mines and mineral resources—

Environmental aspects—Alaska. I. Gray, John E., 1956–. II. Sanzolone, R.F.

III. Bailey, Elizabeth A. IV. Series.

TD196.M4E58 1997

[QE75.B9]

551.9′09798—dc20 96–13189

CIP
III

CONTENTS

Introduction ........................................................................................................................ 1

Geochemical Processes—How Metals Enter Environments Downstream

From Mineral Deposits......................................................................................... 2

Background Geochemical Studies—The Starting Point ............................................ 2

Studies of Mineral Deposits Rich in Heavy Metals ........................................................... 3

Natural Environmental Effects of Silver-Lead-Zinc Massive Sulfide Deposits

in the Northwestern Brooks Range....................................................................... 3

Acid- and Metal-Rich Waters Associated with Iron-Copper-Zinc Massive

Sulfide Deposits in Prince William Sound........................................................... 7

Environmental Geochemistry of Mercury Mines in Southwestern Alaska........................ 14

Environmental Geochemistry of Alaskan Gold Deposits................................................... 19

Gold-Bearing Quartz Veins in the Pacific Gulf Coastal Forest Ecoregion ................ 19

Placer Gold Deposits of the Fairbanks and Nome Districts ....................................... 23

Geochemistry of Surface Waters Draining Alaskan Chromite Deposits ........................... 27

Radioactivity Concerns of Uranium and Thorium Deposits at Bokan Mountain,

 Southeastern Alaska ................................................................................................... 31

Summary............................................................................................................................. 35

References Cited................................................................................................................. 37

Glossary.............................................................................................................................. 39

FIGURES

 1. Map showing location of silver-lead-zinc deposits in the northwestern Brooks Range, Alaska ................................ 3

 2. Photographs in the northwestern Brooks Range, of Red Dog Creek mineral deposit prior to mining,

and of intense red-weathering zones near Drenchwater Creek.............................................................................. 4

 3. Plots demonstrating how water from Discovery Creek affects dissolved zinc in lower Drenchwater Creek ............. 6

 4. Photograph of a bright-orange iron-oxide layer along False Wager Creek, which drains Drenchwater deposit

on east side............................................................................................................................................................. 7

 5. Photograph of mineralized rock from a volcanic-rock-hosted massive sulfide deposit showing veins

with abundant chalcopyrite and pyrrhotite, Prince William Sound ....................................................................... 8

 6. Photograph of abandoned tailings piles (background) near the Dutchess mine ......................................................... 9

 7. Map showing location of massive sulfide deposits studied, Prince William Sound ................................................... 9

 8. Photograph of water effluent discharging from base of tailings piles at the Dutchess mine ...................................... 11

9. Photograph of tailings and effluent from the Beatson mine washing into Prince William Sound,

and view of flooded Beatson pit............................................................................................................................. 12

10. Map showing location of mercury mines and deposits in southwestern Alaska......................................................... 14

11. Photograph of rock sample containing the mercury ore mineral cinnabar ................................................................. 15

12. Schematic diagram showing most important sources of mercury............................................................................... 16

13. Photograph of heavy-mineral sample, showing abundant cinnabar particles ............................................................. 17

14. Plot of mercury in fish muscle versus mercury in fish liver for fish collected throughout southwestern Alaska ....... 18

15. Map showing location of gold vein deposits of the Pacific Gulf Coastal Forest Ecoregion....................................... 19

16. Photograph showing vein containing quartz and pyrite, and microscopic gold.......................................................... 20

CONTENTS

III
IV CONTENTS

17. Photograph of open-pit cut, Alaska-Juneau mine, near Juneau, Alaska ..................................................................... 21

18. Photograph showing geologists sampling waters draining an adit from an abandoned gold mine in

southern Alaska...................................................................................................................................................... 22

19. Map showing location of gold placers in Alaska ........................................................................................................ 24

20. Photograph showing placer operation near Fairbanks ................................................................................................ 25

21. Photograph of Red Mountain chromium deposit, showing color and vegetation contrast between

 ultramafic rock and vegetated soil ........................................................................................................................ 27

22. Photograph showing a seam of black chromite ore layered within the ultramafic rocks at Red Mountain................ 28

23. Location map of the Alaskan chromium occurrences studied .................................................................................... 29

24. Photograph showing water flowing from an abandoned chrome mine....................................................................... 30

25. Map showing location of Bokan Mountain uranium deposits, southeastern Alaska .................................................. 32

26. Photograph of the granitic intrusion at Bokan Mountain............................................................................................ 33

27. Photograph showing previous mining of uranium ore at the Ross-Adams uranium mine ......................................... 33

28. Plot of dissolved metal concentrations in water versus water pH for several Alaskan deposit types......................... 36

TABLES

1. Water standards used for reference in these studies.................................................................................................... 5

2. Geochemical data summary of mineral deposits studied............................................................................................ 36
1

Environmental Studies of Mineral Deposits in Alaska

Edited by John E. Gray and Richard F. Sanzolone

INTRODUCTION

Mining of minerals and metals is important in all industrialized and developing countries. In the United States, mining of metallic mineral deposits is conducted in most States,

including Alaska. In the past century, much of the mining

has concentrated on the extraction of metals necessary for

the economic or industrial development of societies, for

example, gold, silver, iron, copper, lead, zinc, chromium,

mercury, tin, cobalt, molybdenum, nickel, and uranium.

Other metals such as arsenic, cadmium, and selenium are

often enriched in mineral deposits and recovered as byproducts. Because many of these metals can be toxic to

plants, animals, and humans, their interaction with the environment is a national concern. To address this concern, studies of natural and man-made environmental interactions of

metals before, during, and after mining have become

increasingly important to society.

The economic success of any mineral deposit

depends on a clear understanding of its geology, mineralogy, and geochemistry, because these characteristics aid

in locating, developing, and extracting metals and minerals

from ore deposits. These characteristics also affect surrounding environments, because metals can be carried

downstream from the deposits and into local ecosystems.1

With a thorough understanding of the characteristics of

mineral deposits and their downstream effects, scientists

can predict potential environmental problems and identify

solutions to these problems.

To evaluate environmental concerns, scientists measure

metal concentrations in rock, soil, stream-sediment, water,

plant, and sometimes fish samples collected around mines

and mineral deposits. Metal concentrations in these samples

are typically compared to Federal and State standards, as

well as to local background concentrations. These measurements are the initial steps toward identifying environmental

contamination problems associated with mineral deposits,

both prior to, and resulting from mining.

1Italicized terms are defined in the Glossary; see page 39.

The most important environmental concerns resulting from weathering and mining of mineral deposits are

increased acid and metal concentrations downstream that

can potentially degrade drinking water and wildlife

habitat. Thus, the primary objectives of the studies presented here are to:

determine metal and acid concentrations in samples

collected downstream from mineral deposits,

assess the degree of metal contamination in local

streams due to weathering and mining of the deposits,

and

evaluate environmental effects related to the mineral

deposits.

Such studies are particularly important in Alaska: a

number of known mineral deposits exist that have not yet

been developed, and these studies may be useful for future

mining, monitoring, and remediation programs within the

State. These studies may also be useful for evaluation, development, and remediation of mineral deposits of similar type

in similar geographic and geologic settings.

The U.S. Geological Survey (USGS) is working with

several agencies in Alaska, including the U.S. Fish and

Wildlife Service, U.S. Forest Service, National Park Service,

and Alaska native corporations, to evaluate the environmental effects of mineral deposits and their mining. In cooperation with these agencies, the USGS has the unique ability to

integrate aspects of geology, mineralogy, and downstream

geochemistry of mineral deposits in Alaska and identify any

environmental hazards related to these deposits. Studies of

the geology, mineralogy, and geochemistry of mineral

deposits can be integrated with local climatic, hydrologic,

and topographic conditions to address land use and environmental issues. This publication summarizes the results from

some of the first environmental studies of mineral deposits in

Alaska conducted by the USGS. Some of the text is technical, and a glossary of some technical terms is provided.

These technical terms are in italics when first mentioned

throughout the text. 
2 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

GEOCHEMICAL PROCESSES—HOW METALS ENTER ENVIRONMENTS DOWNSTREAM 

FROM MINERAL DEPOSITS

Rocks and minerals exposed at or near the surface of the

Earth undergo changes in color, form, and chemical composition. This process, called weathering, is primarily the result

of the action of air, wind, water, snow, ice, and biological

activity on the rocks and minerals in mined and unmined

mineral deposits. Weathering can result in the formation of

acid water and conversion of metals into water soluble

forms. These acid- and metal-rich waters are commonly

referred to as acid drainage. Formation of acid drainage

around mineral deposits is primarily related to oxidation of

sulfide minerals, especially pyrite (iron sulfide), that produces strong acids like sulfuric acid. Many heavy metals,

including arsenic, copper, lead, zinc, and cadmium, contained within sulfide minerals in the mineral deposits, are

more soluble in water containing abundant acid. When these

acid- and metal-rich waters flow downstream from a mineral

deposit, they may be an environmental concern, if they

adversely affect local wildlife habitat or human health.

At the same time that rocks and minerals are weathering, they are also being eroded, transported, and redeposited

downstream. During this erosion process, the physical and

chemical changes of the rocks and minerals continue at the

site of the mineral deposit, which is the primary source of the

metals, as well as in streams below the deposits. Therefore,

acid- and metal-rich waters will continue to form until these

metal sources are removed by natural or human processes.

BACKGROUND GEOCHEMICAL

STUDIES—THE STARTING POINT

To determine if metal concentrations around mineral

deposits are of environmental concern, scientists collect a

series of samples, chemically analyze these samples for

metal concentrations, and then determine which metal concentrations are “normal or usual” and which are “high or

unusual.” Materials sampled for study are usually stream

water, stream sediment, soil, and sometimes fish and plants.

The initial step in mineral deposit environmental studies is to

collect samples upstream from such mineral deposits, or

from areas where mineral deposits are not known. Samples

collected from such unmineralized areas are referred to as

“background” samples. When these background samples are

chemically analyzed, they provide the chemical concentrations that are considered normal or usual and are unaffected

by mineral deposits or mining. These background samples

provide scientists with a reference or starting point against

which to compare chemical data from samples collected

downstream from mined and unmined mineral deposits. In

many instances, samples collected downstream from mineral

deposits contain high metal concentrations that greatly

exceed those in background samples. These high concentrations must be closely evaluated to determine if the environment has been adversely affected. In the following studies,

data are presented to examine metal concentrations and

related hazards around several types of mineral deposits.

2 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA
STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS 3

ALASKA

Area of

fig. 1

Kotzebue

Drenchwater

Lik

Red Dog

GATES OF THE ARCTIC

NATIONAL PARK

NOATAK NATIONAL PRESERVE BROOKS RANGE

NATIONAL

PETROLEUM RESERVE

IN ALASKA

68 ̊

164 ̊

0 50 100 KILOMETERS

STUDIES OF MINERAL DEPOSITS 

RICH IN HEAVY METALS

Mineral deposits containing large amounts of sulfide

minerals are of environmental concern because heavy

metals such as copper, lead, zinc, and cadmium are highly

concentrated in these deposits. Mineral deposits containing

such large amounts of sulfide minerals are commonly

referred to as massive sulfide deposits. The State of Alaska

contains several types of massive sulfide deposits. The

massive sulfide deposits studied here are (1) those found

primarily in sedimentary rocks in the northwestern Brooks

Range and (2) those closely associated with volcanic rocks

or lavas in Prince William Sound.

NATURAL ENVIRONMENTAL EFFECTS

OF SILVER-LEAD-ZINC MASSIVE SULFIDE

DEPOSITS IN THE NORTHWESTERN 

BROOKS RANGE

Silver-lead-zinc massive sulfide deposits in the northwestern Brooks Range consist of layers rich in sulfide minerals that are dispersed in black shale and chert. The

dominant minerals are sphalerite (zinc sulfide), silver-rich

galena (lead sulfide), pyrite, and marcasite (iron sulfides).

The deposits currently under study in the Brooks Range are

Lik, Drenchwater, and Red Dog (Kelley, 1995) (fig. 1). At

Red Dog, one of the largest zinc deposits in the world, mining of lead and zinc began in 1990 and continues today. The

Lik and Drenchwater deposits have not been mined. All

three deposits are exposed at the surface and were discovered by the presence of orange staining on surrounding hillsides or by the presence of significant heavy metal

concentrations in streams draining the deposits (fig. 2).

Figure 1. Location of silver-lead-zinc massive sulfide deposits in the northwestern Brooks Range, Alaska.
4 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Figure 2A. Photograph in the northwestern

Brooks Range of Red Dog Creek prior to mining

where it flowed through the mineral deposit. Red

Dog Creek had significant natural heavy-metal contamination that eliminated fish life in the vicinity of

the deposit. The contamination and resulting mineral

stain led to discovery of the Red Dog deposit (photo

by C.G. Mull). 

What are the environmental issues of the Brooks

Range massive sulfide deposits?—The Brooks Range

massive sulfide deposits have the potential to form acidand metal-rich waters that can carry high concentrations of

toxic metals such as lead, zinc, and cadmium. Several

thousand people living in the surrounding region traditionally rely on subsistence hunting and fishing for food

sources. These silver-lead-zinc massive sulfide deposits

can be a potential hazard to residents and wildlife, if drainage from these deposits enters streams and rivers that support local wildlife habitat. To evaluate stream water

quality near the deposits, scientists measured concentrations of metals and pH in water collected from streams surrounding these silver-lead-zinc deposits.
STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS 5

Table 1. Water standards used for reference in these studies.

[Concentrations are in ppb (micrograms per liter); --, standard has not been established]

Water quality downstream from massive sulfide

deposits is significantly affected.—Data from the Drenchwater deposit indicate that stream waters draining the

deposit have low pH values (indicating that they are acidic),

and dissolved concentrations of aluminum, arsenic, cadmium, copper, iron, lead, manganese, nickel, and zinc are

several orders of magnitude greater than that in water samples collected upstream (backgrounds) from the deposit (fig.

3). The most acidic waters collected range in pH from 2.8 to

3.1 and contain as much as 95,000 ppb (parts per billion)

aluminum, 26 ppb arsenic, 270,000 ppb iron, 8 ppb cadmium, 260 ppb copper, 10 ppb lead, 3,400 ppb manganese,

290 ppb nickel, and 2,600 ppb zinc; these values are all significantly above background concentrations (Kelley and

Taylor, 1996). Sulfate concentrations (1,180 ppm (parts per

million)) are also high. Although the deposits are rich in silver, water samples contain low silver concentrations (< 0.1

ppb). Locally, the iron- and sulfate-rich waters have precipitated a bright-orange iron-oxide layer that cements the

stream pebbles and cobbles on the creek bottom (fig. 4).

Although metal concentrations in waters draining the

Drenchwater deposit are higher than streams in unmineralized areas, many metals are still present at levels below the

State of Alaska drinking water standards. Levels of cadmium, copper, and zinc exceed the instream criteria maximum concentrations (CMC) that the U.S. Environmental

Protection Agency (EPA) indicates may acutely affect

aquatic life (table 1).

________________________________________________

Element EPA criteria State of Alaska

 maximum maximum

 concentration contaminant

 (CMC)1 level (MCL)2

________________________________________________

Arsenic 360 50

Antimony -- 6

Mercury 32.4 2

Copper 18 1,000

Lead4 82 --

Zinc4 120 5,000

Cadmium4 3.9 5

Iron -- 300

Sulfate -- 250,000

Chromium III 1,700 5100

Chromium VI 16 --

________________________________________________

1CMC is the Environmental Protection Agency’s water quality criteria to protect against acute effects in aquatic life and

is the highest instream concentration of a toxic pollutant consisting of a 1-hour average not to be exceeded more than

once every 3 years on the average.

 2MCL is the maximum concentration allowed by the State

of Alaska in public drinking water systems. Concentrations

listed for copper, zinc, iron, and sulfate are secondary

MCL’s that are reasonable totals and provide a general

guideline for public drinking water systems.

 3The CMC for mercury in seawater is 2.1 ppb.

 4These element standards vary with water hardness. Values listed are for a water hardness of 100, which is similar to

that for streams studied here.

 5Standard is for total chromium concentration.

Figure 2B. Photograph in the northwestern Brooks Range looking west across Drenchwater Creek. The weathering of pyrite has

resulted in intense red-weathering zones.
6 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Drenchwater

Drenchwater Creek

Discovery

Creek

N

1,400

1,200

1,000

800

600

400

200

0

ZINC, IN PARTS PER BILLION

8

pH

7

6

5

4

0 1 2 KILOMETERS

The Red Dog massive sulfide deposit contributes high

acid and metal contents to stream waters, similar to the

Drenchwater deposit. The only significant difference

between the two is the higher metal concentrations in Red

Dog waters relative to Drenchwater. Water quality data

from streams draining the Red Dog deposit prior to mining

(Dames and Moore, 1983; Runnels and others, 1992) reveal

that the waters were acidic (as low as a pH of 3.5) and contained toxic levels of cadmium (as much as 800 ppb), lead

(2,250 ppb), and zinc (272,000 ppb). These concentrations

exceeded the drinking water standards recommended by the

State of Alaska (5 ppb Cd; 15 ppb Pb; and 5,000 ppb Zn)

and the EPA-CMC standards (table 1). Other metals, such

as aluminum, chromium, copper, iron, manganese,

mercury, nickel, and silver, slightly exceeded EPA-CMC

standard. Streams immediately draining the Red Dog

deposit did not support any significant biota, such as fish,

suggesting that waters were apparently toxic to most

aquatic life prior to mining. Stream water quality 15–20 km

downstream of the deposit was also significantly affected:

zinc and cadmium concentrations were well above the recommended CMC concentrations.

The higher metal concentrations of Red Dog waters

relative to Drenchwater are due primarily to the greater

amount of sulfide minerals present in the Red Dog deposit

and the greater extent of exposure of sulfide minerals to

weathering at the surface.

When geology differs, so does the water quality.—The

Lik deposit yields waters that are near-neutral to neutral, and

concentrations of all metals except zinc are low relative to

Drenchwater and Red Dog. Stream waters collected downstream from Lik have pH values of 6.2 to 8.1. Only one sample from a small tributary contained concentrations of

cadmium (5 ppb) and zinc (2,000 ppb) that are comparable

to levels detected below the Drenchwater deposit. Zinc was

the only metal that was consistently high in water samples

below the deposit, ranging from 380 to 2,000 ppb. 

Differences in chemistry between the Drenchwater and

Lik deposits may be attributed to the presence of carbonate

rocks, such as limestone, surrounding the Lik deposit. Carbonate rocks tend to neutralize acid in the water and, because

metals are more soluble in water containing significant acid,

these near-neutral waters have a lesser ability to transport

most metals in solution.

Figure 3. Plots demonstrating how the stream water from Discovery Creek, which drains mineralized areas, affects the

dissolved zinc in lower Drenchwater Creek. Aluminum, cadmium, copper, iron, lead, manganese, and nickel show variations in concentrations similar to zinc that reflect the input of water contaminated by metals naturally weathering from the

mineralized area. In addition, the pH of water downstream from the deposit dramatically decreases (acidity increases).

Data were collected in July 1994.
STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS 7

ACID- AND METAL-RICH WATERS

ASSOCIATED WITH IRON-COPPER-ZINC 

MASSIVE SULFIDE DEPOSITS IN

PRINCE WILLIAM SOUND

Massive sulfide deposits in Prince William Sound consist of iron-, copper-, and zinc-rich sulfide minerals in and

near volcanic rocks. Many of the deposits were mined from

about 1900 to 1930, but have since been abandoned. These

abandoned mines are located in the Chugach National Forest

and on private lands within the forest.

Rocks in the Prince William Sound region are dominantly sandstone and slate, with some basalt. The massive

sulfide deposits are most common in basalt, but are found

also in nearby sedimentary rocks. The primary sulfide

minerals are pyrite, pyrrhotite, chalcopyrite, and sphalerite

(fig. 5). Minor galena is present in some deposits. Sulfide-rich bodies range in size from a few centimeters to 90

m wide and a few hundred meters long.

Workings range from small prospect trenches to mines

with tunnels hundreds of meters long. The Beatson mine

contains more than 4 km of tunnels and a 300 m diameter

open pit. Small tailings piles, about 10 to 20 m high, are

found at most mine sites (fig. 6). These tailings generally are

bright red as a result of the weathering of sulfide minerals.

Bright-green to black moss covers metal-rich soils where the

landscape was stripped for mining. Mine waste piles, underground workings, and unmined ore can potentially form

acidic and metal-rich effluent that can enter local streams

and rivers; such effluent may eventually reach Prince William Sound, which could present a problem to this local

marine environment. Prior to this study, no detailed hydrogeochemical data have been collected to determine the

extent of acid-mine drainage to Prince William Sound.

Stream waters from tailings versus mine adit

waters.—Waters were collected within, upstream from,

and downstream from mines located in three areas:

LaTouche Island (Beatson, Blackbird, Duke, and Dutchess

mines), Knight Island (Barnes Cove prospect and Rua

Cove mine), and Port Fidalgo (Schlosser, Fidalgo, and

Threeman mines) (fig. 7). The concentration of metals in

surface waters collected from unmineralized areas (background concentrations) is largely controlled by the chemistry of the rocks and soils. Metal concentrations are

generally low in waters collected from background sites

and are 0.3 to 0.6 ppb copper, 0.8 to 1.4 ppb zinc, <0.1 ppb

cadmium, <0.5 ppb lead, <20 ppb iron, and 4 ppm sulfate.

Background waters generally have pH values near 7.

Figure 4. A bright-orange iron-oxide layer locally covers the bottom and cements stream pebbles and cobbles along False Wager

Creek, which drains the Drenchwater deposit on the east side. The

orange part of the stream in this photo is about 1.5–2 m wide.

What has the Brooks Range massive sulfide data told

us?—These results show that the primary factors affecting

water chemistry are the extent of exposure of the deposits,

the amount of sulfide minerals present, and the presence or

absence of carbonate rocks. In the absence of carbonate

rocks, silver-lead-zinc massive sulfide deposits in the

Brooks Range can produce significant naturally occurring

heavy-metal concentrations in downstream waters. Carbonate rocks are not present at the Red Dog and Drenchwater

deposits, and waters are highly acidic and metal rich. In contrast, carbonate rocks are abundant at the Lik deposit, and

waters are near-neutral and contain low concentrations of

most metals except zinc. 

These data are useful for predicting the environmental

effects likely to result from natural weathering of massive

sulfide deposits and from possible future mining of such

deposits. Furthermore, the data enable mine planners to better anticipate, plan for, and mitigate potential environmental

problems, and are useful for devising realistic plans for

remediation and monitoring programs.
8 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Figure 5. Mineralized rock from a volcanic-rock-hosted massive sulfide deposit showing veins

with abundant chalcopyrite and pyrrhotite, Prince William Sound.

8 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA
STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS 9

61 ̊

149 ̊ 147 ̊

60 ̊

ALASKA

Area of

figure

Turnagain Arm

Whittier

Seward

Valdez

Kenai Peninsula

Cordova

Contact

fault

Port Wells

Contact fault

Glacier

Island Port Valdez

Port Fidalgo

PRINCE

WILLIAM

SOUND

Knight

Island

Latouche

Island

Montague Island

Threeman

Fidalgo

Schlosser

Rua Cove

Barnes

Cove

Beatson, Blackbird,

Duke, Dutchess

0 50 KILOMETERS

Figure 6. Abandoned tailings piles (background) near the Dutchess mine.

Figure 7. Location of massive sulfide deposits studied (crossed pick and hammer symbol), Prince

William Sound.
10 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Waters containing the highest metal concentrations in

the Prince William Sound area were collected from the base

of tailings piles (fig. 8). These waters contain as much as

3,600 ppb copper, 3,300 ppb zinc, 21,000 ppb iron, 220 ppb

lead, 10 ppb cadmium, and 311 ppm sulfate and have pH values as low as 2.6 (Goldfarb and others, 1996). Waters collected directly from mine adits contained lower metal

contents, and pH values of about 6: adit waters contained as

much as 1,400 ppb copper, 3,100 ppb zinc, 310 ppb iron, 27

ppb cadmium, 0.9 ppb lead, and 166 ppm sulfate, but most

adit waters contained significantly lower metal concentrations. The much higher metal concentrations and acidity in

waters from the tailings piles are the result of weathering of

sulfide minerals in the tailings.

Acid- and metal-rich waters emanating from these

massive sulfide deposits are rapidly diluted downstream by

larger streams. The large streams below the mines have

near-neutral pH values, and the amount of acid-mine drainage from the deposits is too small to affect the acidity, metal

loadings, and water quality of these larger streams.

The flooded pit at the Beatson mine is about 500 m

from the shoreline of Prince William Sound and represents

a potential heavy-metal source. Water discharging from the

base of the pit (fig. 9) has a pH of 6.5, and waters in the pit

have a pH of 7.3. Such near-neutral pH values limit the solubility of most metals, and thus, the amount of metal that

will be transported in water downstream to Prince William

Sound. Water discharging from the pit contains 30 ppb

iron, 21 ppb copper, 39 ppb zinc, and 6.5 ppm sulfate.

Although these metal concentrations are not as elevated as

those collected downstream from other massive sulfide

deposits, the volume of water in the pit and the drainage

emanating below the pit could deliver a large enough

quantity of metal to the near-shore marine environment to

possibly damage Prince William Sound.

Why do we care about massive sulfide deposits in

Prince William Sound?—Many of the iron-copper-zinc

massive sulfide deposits in the Prince William Sound area

produce metal-rich waters as they weather. Metal concentrations and the pH of the acid-mine drainage will depend on a

number of factors, including the amount and type of sulfide

minerals present, extent of weathering, local hydrology, and

the acid-neutralizing capacity of the rocks. Our studies show

that on a local scale, especially where surface waters flow

through tailings piles, acid-mine drainage is a concern in

Prince William Sound.

Water data show that prior to emptying into major

stream channels, surface waters flowing away from most of

the mine workings exceed recommended EPA-CMC concentrations for copper, lead, zinc, and cadmium (table 1).

Furthermore, much of the mine discharge exceeds the State

of Alaska drinking water limits of 5 ppb cadmium, 1,000 ppb

copper, and 300 ppb iron; in addition, mine effluent is often

more acidic than the recommended drinking water pH range

of 6.5 to 8.5. Therefore, at least locally, surface water may

not be suitable for human consumption. 

Whether any of these abandoned mines pose a threat to

the downstream marine life of Prince William Sound is presently unknown. However, acid- and metal-rich waters

clearly exit the base of the Beatson mine pit and drain into

Prince William Sound a few hundred meters below the mine.

Metal concentrations in these waters are about 10 times

higher than in waters from background sites. Because marine

life is especially sensitive to elevated heavy-metal concentrations, additional analysis of near-shore waters for metal

enrichments is warranted.

10 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA
STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS 11

Figure 8. Water effluent discharging from base of tailings piles at the Dutchess mine.
12 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Figure 9A. Tailings and effluent (foreground) of the Beatson mine, washing into Prince William Sound (background).
STUDIES OF MINERAL DEPOSITS RICH IN HEAVY METALS 13

Figure 9B. View of the Beatson mine flooded pit.
14 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

64 ̊

Mercury mine

Mercury deposit

Study

area

ALASKA

Sleetmute

Aniak

Bethel

Dillingham

Kuskokwim

Bay

Bristol

Bay

Iliamna

Lake

Kuskokwim River

Yuk on

River

0 100 KILOMETERS 50

156 ̊ 160 ̊ 164 ̊

62 ̊

60 ̊

Figure 10. Location of mercury mines and deposits in southwestern Alaska.

ENVIRONMENTAL GEOCHEMISTRY 

OF MERCURY MINES IN 

SOUTHWESTERN ALASKA

Mercury-rich mineral deposits in Alaska are another

type of deposit under investigation for natural and miningrelated heavy-metal concentrations in the environment.

Mercury deposits are scattered over a wide region in southwestern Alaska covering several tens of thousands of square

kilometers (fig. 10). The mercury sulfide mineral cinnabar

is the most common mercury ore mineral in the deposits (fig.

11), but liquid mercury also occurs naturally at some localities. Several of the mercury deposits have been mined, but

most of the deposits are small and undisturbed. None of the

mercury mines in Alaska are currently operating, due to economic factors. Mercury is used in the manufacturing of electrical instruments, fungicides, pharmaceuticals, and

munitions, in the production of paper, and in the extraction

of gold (amalgamation of gold) in mining. 

Should we be concerned about mercury mineral

deposits in southwestern Alaska?—Mercury is a heavy

metal that has no known metabolic function and is toxic to

living organisms. In humans, mercury adversely affects the

central nervous system and internal organs such as the kidneys. In streams and lakes, bacterial activity converts mercury in sediments from inorganic compounds (such as

cinnabar) to organic forms (such as methylmercury).

Organic mercury compounds are easily absorbed by organisms and are more hazardous than inorganic forms.

The primary sources of mercury are naturally occurring

mineral deposits, rocks, soils, and volcanic eruptions, as well

as man-made industrial sources such as factory effluents and

airborne incinerations. Southwestern Alaska has no major

sources of industrial mercury; however, mercury is highly

concentrated around mineral deposits in the region. Thus, the

presence of mercury deposits in southwestern Alaska is a

potential hazard to residents and wildlife because drainage

from the deposits enters streams and rivers that are part of

local ecosystems (fig. 12). To evaluate the environmental

concerns of these mercury deposits, the concentration of

mercury was measured in sediment, water, soil, vegetation,

and fish collected around some of the mercury deposits.

These data were then compared with those from streams in

unmineralized (background) areas.
ENVIRONMENTAL GEOCHEMISTRY OF MERCURY MINES IN SOUTHWESTERN ALASKA 15

Measuring mercury levels in stream sediments,

stream water, and fish.—Stream-sediment samples collected near some mines contain total mercury concentrations

in excess of 5,000 ppm (Gray, 1994). Stream-sediment samples collected from streams in local unmineralized areas typically contain less than 1 ppm mercury, indicating that the

samples collected near the mines are highly enriched in mercury. These high mercury concentrations in stream sediments near the mines are the result of erosion of cinnabar

into the streams. Cinnabar is resistant to weathering, and

thus, it remains in streams for long periods of time (fig. 13).

Stream waters below the mercury mines generally are

neutral to slightly alkaline with pH values of about 7 to 8.

The formation of acid drainage below some mineral deposits

containing sulfide minerals can be of concern; however, cinnabar is highly insoluble in water and does not easily form

acid drainage during weathering. Thus, acid formation in

streams below the mercury mines and deposits in southwestern Alaska is probably insignificant.

Figure 11. Rock sample containing the mercury ore mineral cinnabar (red mineral). Pencil point for scale.

Samples of stream water collected below mercury

mines contained as much as 0.75 ppb mercury, whereas

background stream and river waters in the region typically

contain less than 0.10 ppb. These mercury concentrations

are below the 2.0 ppb drinking water standard recommended by the State of Alaska and the 2.4 ppb instream

EPA-CMC standard (table 1).

Although cinnabar is highly insoluble in water, the

water data indicate that minor amounts of mercury are converted to forms that are soluble in water, probably organic

forms of mercury, that are easily absorbed by organisms,

such as fish, living in the stream environment. For this reason, fish were collected throughout southwestern Alaska and

analyzed for mercury to evaluate the potential for mercury to

enter local food sources and the food chain. Mercury concentrations were measured in fish muscle samples (edible fillets)

and livers. Maximum mercury concentrations in the muscle

samples of freshwater fish collected downstream from mercury mines were about 0.6 ppm (wet weight) and about 1.3

ppm in the liver samples (fig. 14) (Gray and others, 1994,

1996). These concentrations are considered elevated because

similar fish collected from background streams in southwestern Alaska contained only about 0.2 ppm mercury. Most of

the mercury in the fish (> 90 percent) was the highly toxic

organic form of mercury, methylmercury. Although the fish

collected downstream from the mines contain mercury concentrations higher than background levels, mercury contents

in the edible portions of the fish were below

the 1.0 ppm limit established by the Food and

Drug Administration (FDA).

Mercury concentrations were also measured in salmon collected from large rivers in the

region because these fish are foods of local

residents and sportsmen. Mercury concentrations in salmon muscle samples were low,

less than 0.1 ppm (Gray and others, 1996),

well below the recommended FDA

limit. These low mercury concentrations are understandable because

salmon spend much of their

lives in the ocean and are in

contact with stream

waters in southwestern

Alaska only when hatching and spawning.
16 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Mercury Cycle

Sources:

1. Industrial

(organic Hg)

2. Mines & deposits

(inorganic Hg)

Water Supplies

Food Chain:

Mercury increases in

concentration as it 

moves up the food chain

2

3

1

Figure 12. Schematic diagram of mercury cycle showing the most important sources of mercury—industrial, volcanoes, and mineral deposits such as those in southwestern Alaska. When mercury from mineral deposits erodes into streams, toxic mercury compounds can be

absorbed by fish and eventually consumed by humans.
ENVIRONMENTAL GEOCHEMISTRY OF MERCURY MINES IN SOUTHWESTERN ALASKA 17

What are the answers to environmental questions

about the mercury deposits?—Stream-sediment, streamwater, soil, vegetation, and fish samples collected near the

mines have elevated concentrations of mercury. Cinnabar in

the mines is the dominant source of this mercury. Erosion of

the cinnabar around the mines results in highly elevated

mercury concentrations in stream sediments, soils, and vegetation. The elevated mercury concentrations in fish downstream from the mines indicate that mercury is being

converted from inorganic mercury, such as cinnabar, to

organic mercury that is more biologically available. The

mercury is then transferred to water and to food sources for

the fish, such as larvae, insects, and other small aquatic

organisms that live in the streams. Mercury or other contaminant can concentrate in tissues of organisms when it is taken

up more rapidly than the organism can eliminate it, a process

called bioaccumulation. When mercury enters the food

chain it tends to concentrate in the highest predators, a process called biomagnification; thus, mercury concentrations

in fish are useful for evaluating levels of mercury in the food

chain that can eventually affect humans. The results of this

study suggest that, although samples of stream sediment,

water, soil, and vegetation collected near the mines contain

elevated mercury concentrations, concentrations of mercury

in fish indicate minor, local effects on food chains.

Levels of mercury in soil and vegetation around

mines.—Soil and vegetation samples collected around

mines also contained higher mercury concentrations than

local background samples. Soils around mines contained as

much as 1,500 ppm mercury, whereas background soil

samples generally contained less than 1 ppm mercury.

Alder leaves collected near mines contained from 0.03 to

0.97 ppm mercury (dry weight), compared to alder leaves

from background sites containing less than 0.2 ppm. Scientists were most interested in the amount of the toxic

methylmercury in plants that could be consumed by

browsing animals in areas near the mines. Unlike fish,

where the highly toxic methylmercury represents the large

majority of the total mercury, only a small fraction of the

mercury in vegetation is methylmercury, generally less than

5 percent. It is unlikely that mercury contents in such minor

amounts represent a significant health concern to wildlife

that consume such vegetation.

Figure 13. Heavy-mineral sample in a gold pan showing abundant cinnabar particles.
18 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

1.0

0.8

0.6

0.4

0.2

0

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

MERCURY, IN PARTS PER MILLION WET WEIGHT IN FISH MUSCLE

MERCURY, IN PARTS PER MILLION WET WEIGHT IN FISH LIVER

FDA action level for edible fish

Cinnabar Creek Dolly Varden and Arctic grayling

Kolmakof River Arctic grayling

Chineekluk Creek Arctic grayling

Background Arctic grayling

Salmon

EXPLANATION

Figure 14. Plot of mercury in fish muscle versus mercury in fish liver for fish collected throughout southwestern Alaska.
ENVIRONMENTAL GEOCHEMISTRY OF ALASKAN GOLD DEPOSITS 19

ENVIRONMENTAL

GEOCHEMISTRY OF

ALASKAN GOLD DEPOSITS

Mining of gold deposits has been a major industry in

Alaska since the early 1900’s. Both large gold vein deposits

such as the Alaska-Juneau mine, near Juneau, and large

placer gold districts, such as those near Fairbanks and Nome,

have been economically important in the past and will continue to be important in the future. Heavy metals such as

arsenic, copper, lead, zinc, and cadmium are associated with

many of the gold deposits. The following two studies evaluate environmental concerns of heavy metals in streams and

rivers downstream from Alaskan gold deposits.

GOLD-BEARING QUARTZ VEINS

IN THE PACIFIC GULF

COASTAL FOREST ECOREGION

The Pacific Gulf Coastal Forest Ecoregion, as defined

by the U.S. Forest Service, includes the coastal regions of

south-central and southeastern Alaska along the Gulf of

Alaska. In south-central Alaska, these lands are composed

of the Kodiak Mountains, Kenai-Chugach Mountains, and

the Gulf of Alaska coastal plain. In southeastern Alaska,

geographic provinces of the ecoregion include the Boundary Ranges, Coastal Foothills, and Chilkat-Baranof Mountains (fig. 15).

Rocks in this region are predominantly marine sandstone and shale that are intruded by minor granitic rocks.

Gold-bearing quartz veins are the most widespread mineral

deposit in the region (fig. 15). The veins contain less than 3

percent sulfide minerals (fig. 16) and cut both the sedimentary and granitic rocks. The sulfide minerals are typically

pyrite, arsenopyrite, chalcopyrite, galena, sphalerite, and

stibnite. Calcite and other carbonate alteration minerals are

adjacent to the veins. Veins range in length from a few tens

of meters to more than a kilometer, with maximum widths of

about 5 m. More than 100 of these gold vein deposits were

mined in the early 1900’s. Mines range from open cuts and

short tunnels at the smaller deposits, to large open pits (glory

holes) at the largest deposits, such as the Alaska-Juneau

deposit (fig. 17).

Southern Alaska Gold Districts

Talkeetna 

8. Willow Creek

Chugach-Kenai Mts

1. Girdwood

2. Hope-Sunrise

3. Moose Pass

4. Nuka Bay

5. Port Wells

6. Port Valdez

7. McKinley Lake

Juneau Gold Belt

 9. Berners Bay

10. Alaska-Juneau,

 Treadwell

11. Endicott Peninsula

Chichagof Island

12. Chichagof

60 ̊

136 ̊ 152 ̊

8

1

2

3

4

5

6

7

12

9

10

11

Anchorage

Seward

Valdez

JUNEAU

ALASKA UNITED STATES

CANADA

WRANGELL

MOUNTAINS

CHUGACH

MOUNTAINS

TALKEETNA

MOUNTAINS

KENAI MTS

BOUNDARY

RANGES COASTAL FOOTHILLS

Prince William Sound

CHILKAT-BARANOF

GULF OF ALASKA MOUNTAINS

PACIFIC OCEAN

Kodiak

Island 0 150 300 KILOMETERS

Figure 15. Location of gold vein deposits of the Pacific Gulf Coastal Forest Ecoregion.
20 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Establishing background concentrations in streams

for the gold vein studies.—Background concentrations for

metals in stream waters that drain unmineralized rocks were

found to be <0.05 ppb silver, <5 ppb arsenic, <1 ppb cadmium, ≤1 ppb copper, ≤20 ppb iron, <1 ppb lead, 0.1 to 0.2

ppb antimony, 3 to 6 ppb zinc, and 0.7 to 1.7 ppm sulfate.

The pH of surface waters varies from 7.2 to 7.9. Waters emanating from weathered, unmined gold vein deposits also contain low heavy-metal and sulfate concentrations. For

example, in the Nuka Bay district (fig. 15, locality 4), surface

waters flowing from small, unmined, gold-bearing veins

contain as much as 6 ppb arsenic and 3.6 ppm sulfate (Cieutat and others, 1994). Concentrations of 140 ppb iron and 4.6

ppm sulfate were measured in a large stream in the Girdwood district (Carrick and Maurer, 1994).

Testing for acid and toxic metals in waters downstream from mines.—Waters emanating from gold mines

(fig. 18) have pH values near neutral, indicating that acid

water formation is minor. The most acidic water collected

had a pH of 6.4, but most waters contained slightly alkaline

pH values, similar to background surface waters collected

throughout the region. Most metal concentrations in the

mine waters are also similar to that of background waters.

However, because pyrite and arsenopyrite are the dominant

sulfide minerals found along with gold at the mines, iron and

arsenic are generally the most elevated metals. In the Nuka

Bay district, a maximum concentration of 130 ppb arsenic

was measured in water immediately downstream from a

small vein and tailings pile. In the McKinley Lake district

(fig. 15, locality 7), water-filled prospect pits contained as

much as 94 ppb arsenic and 650 ppb iron (Trainor and others,

1996). Mine waters collected from both districts contained

as much as 5 ppm sulfate. The stream draining the Girdwood

district contained 8.5 ppm sulfate and 550 ppb iron.

Figure 16. Vein containing quartz (white) and pyrite (brass colored). Microscopic gold is contained within pyrite grains,

but because of its fine-grained nature is not visible. Felt marker for scale.

20 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA
ENVIRONMENTAL GEOCHEMISTRY OF ALASKAN GOLD DEPOSITS 21

The Alaska-Juneau mine was the largest gold lode in

Alaska, with more than 109,000 kg (3,500,000 oz) of gold

produced from 1893 to 1944. Unlike many of the other goldbearing vein deposits in the region, the Alaska-Juneau

deposit contains abundant sphalerite and galena. Most mine

drainage emanates from one tunnel, and this water has a

measured pH of 8 and concentrations of <0.5 ppb silver, 0.6

to 2.7 ppb arsenic, <0.2 ppb cadmium, <2 ppb copper, <100

ppb iron, <2 ppb lead, <0.2 ppb mercury, 39 to 52 ppb zinc,

and 230 to 340 ppm sulfate. Except for sulfate and zinc, these

data are similar to those of background waters collected from

unmineralized areas.

What are the environmental issues related to the gold

vein deposits?—Compared to mine-drainage waters associated with other mineral deposit types, waters emanating

from gold-bearing quartz veins contain low metal concentrations due to the low abundance of sulfide minerals in these

gold-bearing vein deposits and mines. In addition, carbonate

minerals that form adjacent to the veins tend to neutralize the

minor amount of acid produced during weathering of the sulfide minerals. Water pH is consequently maintained near

neutral. In waters of near-neutral pH, most metals have low

solubilities and are not easily transported from the deposits.

Even waters that drain Alaska’s largest lode gold mine contain total base metal concentrations (copper+lead+zinc+cadmium) of less than 100 ppb.

Arsenic and iron are the most commonly enriched metals in waters emanating from mines, and their presence is

related to the sulfide mineralogy of the deposits; but these

metal concentrations in the waters rarely exceed the State of

Alaska maximum levels for drinking water of 50 ppb arsenic

and 300 ppb iron. Although higher concentrations have been

measured in water samples from some localities, effluent

throughout this ecoregion is rapidly diluted when discharged

into larger stream channels. Metal concentrations in waters

that drain Alaska’s largest gold mine are consistently below

the drinking water maximum allowable levels; only sulfate

occasionally exceeds the State limit of 250 ppm.

Figure 17. Open-pit cut at the largest gold vein deposit in Alaska, the Alaska-Juneau mine, near Juneau.
22 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA 22 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Figure 18. Sampling waters draining an adit from an abandoned gold mine in southern Alaska.
ENVIRONMENTAL GEOCHEMISTRY OF ALASKAN GOLD DEPOSITS 23

PLACER GOLD DEPOSITS OF THE

FAIRBANKS AND NOME DISTRICTS

Placer mining has been an important industry in Alaska

since the late 1800’s. Although some placer gold mines are

currently operating in Alaska, many are now abandoned.

Placer mining has produced about 730,000 kg (23,490,700

oz) of gold, which represents more than 70 percent of all

gold produced in Alaska (Swainbank and others, 1995). The

two largest Alaskan placer gold districts, Fairbanks and

Nome, produced about 247,000 kg (7,971,000 oz) and

149,900 kg (4,822,500 oz) of gold, respectively. Because

placer mining has been widespread in Alaska (fig. 19), environmental concerns related to placer mining are addressed

by evaluating the water geochemistry of samples collected

from these two major gold districts.

What are placers?—Placer deposits form in stream

beds, on beaches, in deltas, and in marine sediments when

the action of water erodes rocks and minerals, separating

heavy minerals from lighter ones. Stream placer deposits,

like those in the Fairbanks district, are surficial accumulations of stream rock, gravel, and sediment containing concentrated heavy minerals (fig. 20). Beach and marine

placers, like those found in the Nome district, form near the

mouths of rivers, and similar to stream placers, gold and

other heavy minerals are transported to the seas in rivers

and streams. After the gold and stream sediment are deposited in the marine environment, ocean currents rework the

sediments, concentrating the heavy minerals in deposits

along beaches and in shallow marine settings. Minerals

common in most placer deposits include free gold, and

oxide and sulfide minerals of tin, tungsten,

antimony, copper, zinc, lead, mercury, and

arsenic.

During placer mining, water is used to

separate gold from the sediment. During this

process, the water becomes turbid and muddy.

Present-day placer operations capture this turbid

waste water in nearby, man-made ponds until

enough of the finely suspended sediment and mud has

settled out, and the water can be reused or discharged

back into streams or other water bodies. Because the

objective of placer mining is to remove small

amounts of gold from large volumes of sediment, a significant amount of unwanted or

waste material remains. This waste is composed mostly of rocks, boulders, coarse gravel, and other

heavy minerals (placer tailings) that are commonly mounded

and left in stream valley bottoms.

Environmental issues of placer deposits in

Alaska.—The primary environmental concern from placer

mining is the potential for the generation of acid and metalrich water, but increased water turbidity or the addition of

toxic materials (such as liquid mercury) into the streams may

also degrade stream water quality. Enrichment of metals in

streams below placer mines can affect water quality. Heavy

metals such as arsenic, copper, lead, zinc, and cadmium can

be carried downstream when they are dissolved in water during weathering or can be transported downstream as fine

sediment. These heavy metals can be toxic to life forms

when concentrations are exceedingly high.
24 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Metal concentrations in waters below placer

mines.—To evaluate the adverse effects, metal concentrations in waters collected downstream from placer mines

were measured and then compared to local backgrounds and

State and Federal water quality standards. Stream water samples collected upstream (backgrounds) and downstream

from two placer mines in the Fairbanks district (Fairbanks

and Porcupine Creeks) were analyzed for arsenic, zinc, cadmium, copper, and lead to address these environmental concerns (Ray and others, 1992). Arsenic concentrations in

stream waters on Fairbanks Creek range from 22 to 64 ppb

upstream, and from 62 to 112 ppb below the placer. Arsenic

concentrations in stream water samples from Porcupine

Creek range from <1 to 15 ppb upstream, and from <1 to 20

ppb below the placer deposit (Ray and others, 1992).

Of most significance are the elevated arsenic concentrations in stream waters collected below the placer on Fairbanks Creek compared to the arsenic levels in the

background stream water samples. These elevated arsenic

concentrations are probably related to the weathering of

arsenopyrite, which is common in the placer tailings.

Although the stream water concentrations of arsenic are

below the EPA-CMC standard of 360 ppb (table 1), some

water samples collected from Fairbanks Creek exceed the

50 ppb maximum level of arsenic recommended for drinking water by the State of Alaska (table 1). Acid-water formation around placer deposits in the Fairbanks district does

not appear to be a significant problem because pH values

for the two stream waters are near neutral, ranging from 6.5

to 8.1. Concentrations of other heavy metals in stream

waters are below the EPA-CMC standard and appear to be

of minor concern. 

66 ̊

160 ̊ 150 ̊

60 ̊

ALASKA

Fairbanks

Nome

Norton Sound

Bering Sea

Gulf of Alaska

ARCTIC OCEAN

Yukon Riv er

Principal gold placer 

districts 

Placer gold districts 

studied

EXPLANATION

0 250 500 KILOMETERS

Figure 19. Location of gold placers in Alaska.
ENVIRONMENTAL GEOCHEMISTRY OF ALASKAN GOLD DEPOSITS 25

Figure 20. Placer operation near Fairbanks showing placer tailings piles and settling ponds.
26 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Environmental effects related to water turbidity.—Highly turbid waters often reduce light transmitted to

the stream bottom, reducing photosynthesis. Excessively

turbid waters can smother plant life, destroy habitats for

benthic organisms, and clog the gills in fish. Prior to the mid

1980’s, waste water was not held in settling ponds, but was

often discharged directly back into streams. Today, turbid

water discharges from placer operations are closely monitored, and the downstream effects are generally fairly minor.

Mercury introduced during placer mining.—Liquid

mercury has been used for the extraction of gold (amalgamation of gold) for many years. Amalgamation of gold has

been most often used in placer operations because often the

gold is fine grained. Although gold amalgamation is rarely

used today, some liquid mercury may remain in streams

near old placer operations because it was sometimes

spilled, lost, or discarded.

During the 1980’s and 1990’s, high concentrations of

mercury and other heavy metals were found in marine waters

near the Nome placer deposits. Mercury concerns scientists

the most because it is toxic to life forms and can enter the

food chain and affect the health of wildlife and humans.

Mercury concentrations in seawater collected near the Nome

placer district ranged from <0.05 to 0.48 ppb (U.S. Minerals

Management Service, 1989). Although these mercury concentrations are considered high for seawater, they are below

the 2.1 ppb EPA-CMC standard for seawater (table 1). The

source of mercury was traced to upstream sources of cinnabar and liquid mercury used for gold amalgamation in the

area (U.S. Minerals Management Service, 1989).

Conclusions of the placer studies.—Placer deposits

contain minerals with heavy metals that are potentially

toxic to humans and wildlife, but water quality degradation downstream from placer mines is relatively minimal.

For example, although arsenic concentrations in stream

waters sampled below placers in the Fairbanks district

exceed the State drinking water standard, these arsenic

concentrations are also below the EPA-CMC standard. In

addition, acid-water formation below placer deposits in the

Fairbanks district is minor because measured water pH is

generally near neutral. Mercury concentrations in

seawater near the Nome placer district are higher than in

typical background seawater, but are well below the EPACMC standard. Most other heavy-metal concentrations in

waters near the placers studied here are low and of minor

concern. Continued study of the environmental effects of

placer deposits is important, especially in streams that support wildlife, or in populated areas.
GEOCHEMISTRY OF SURFACE WATERS DRAINING ALASKAN CHROMITE DEPOSITS 27

GEOCHEMISTRY OF SURFACE 

WATERS DRAINING ALASKAN 

CHROMITE DEPOSITS

Most of the world’s chromium is found in ultramafic

rocks. These ultramafic igneous rock complexes consist of

dark, layered rocks that are rich in silica, magnesium, iron,

and calcium, as well as the mineral chromite. These ultramafic rocks generally weather to an orange-brown color due to

the formation of iron oxides, and these rocks typically do not

support vegetation (fig. 21). Chromium ore consists of black

layers or seams that are rich in chromite. Although these

seams vary in thickness from the width of a few chromite

grains to nearly 2 m, only thick seams are mined (fig. 22).

Chromium is used in the manufacturing of steel alloys, metals plating, pigments and dyes, wood preservatives, and as a

catalyst in chemical processes.

There are several chromite deposits throughout Alaska

that are associated with ultramafic rocks. USGS scientists

studied two of these chromite-bearing occurrences (fig. 23).

Red Mountain, located 16 km from the town of Seldovia,

was the largest chromite mine in Alaska, where over 35,000

t of chromium ore was recovered through 1976. Drainage

from the Red Mountain mine enters streams that eventually

run into a saltwater fishery in Kachemak Bay. Siniktanneyak

Mountain (fig. 23), in the western Brooks Range, was the

site of USGS study of a second, small, unmined chromite

seam. At both locations scientists collected water samples

downstream from the mineralized areas (fig. 24), as well as

from local unmineralized (background) areas to determine

water pH, chromium concentrations, and other major- and

trace-metal concentrations.

Figure 21. The Red Mountain chromium deposit, showing the color and vegetation contrast between the

bare, light-orange ultramafic rock (center background), and vegetated soil (left background).
28 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Potential hazards related to chromium deposits.—Weathering of ultramafic rocks produces two types

of surface waters (Barnes and O’Neil, 1969). The most

common type is alkaline with pH values of about 8.3 to

8.6 and is enriched with magnesium bicarbonate. The second and much less common type is a highly alkaline, calcium hydroxide water with pH values of about 11.2 to

11.8. Because most chromium deposits are found in ultramafic rocks, it is important to understand how waters

flowing from such rocks interact with chromite. Although

chromite is resistant to chemical and physical weathering

and highly insoluble in near-neutral surface water, in some

cases, small amounts of chromium can be found in water

as either a trivalent or the highly oxidized hexavalent form

(Hem, 1992). Trivalent chromium is the dominant form in

most surface waters, but in highly oxygenated, alkaline

waters of pH greater than 9, hexavalent chromium predominates. This hexavalent chromium poses the most

environmental concern because it is toxic to humans and

animals (Simon and others, 1994).

Chromium concentrations in surface waters draining

the Alaskan deposits.—Waters flowing from the two Alaskan chromite localities studied are the alkaline, magnesium

bicarbonate type. Measured pH values of 7 to 8 at both

deposits indicate that the streams draining the deposits are

neutral to slightly alkaline. Stream water samples collected

downstream from the Red Mountain mine contain between

0.5 and 1.0 ppb chromium, well below the State of Alaska

drinking water standard of 100 ppb (table 1). Water samples

collected downstream from the Siniktanneyak locality contain chromium below the 0.5 ppb lower limit of determination. Other heavy metals measured in the waters, such as

nickel, copper, lead, and zinc, are also below drinking water

standards and similar in concentration to waters collected

from background sites.

Figure 22. Photograph showing a 60 cm thick seam of black chromite ore layered within the ultramafic rocks at Red

Mountain.
GEOCHEMISTRY OF SURFACE WATERS DRAINING ALASKAN CHROMITE DEPOSITS 29

Stream waters contain low concentrations of chromium.—The low chromium concentrations in waters collected from the Red Mountain mine and the Siniktanneyak

Mountain complex are consistent with the low solubility of

chromium in slightly alkaline surface water. Concentrations

of trivalent and hexavalent chromium were not determined

in these studies because the total chromium contents of the

waters were low and because the water pH values were

below 9. Such waters are unlikely to contain chromium in

the toxic hexavalent form. Results for these two Alaskan

chromite deposits suggest no adverse effect on the quality

of waters emanating from the deposits. In addition, chromium concentrations entering streams below the Red

Mountain deposit are probably not high enough to

adversely affect the fishery near Seldovia, although chromium accumulation in bottom sediments and possible

transference to fish were not evaluated.

ALASKA

Fairbanks

Nome

Bering Sea PACIFIC OCEAN

ARCTIC OCEAN

Yukon Riv er

 Chromium deposits 

and mineral 

occurrences

Chromium occurrences 

studied

EXPLANATION

0 250 500 KILOMETERS

Kuskokwim River

Anchorage

Siniktanneyak

Red Mountain

66 ̊

160 ̊ 150 ̊

60 ̊

Figure 23. Location map of the Alaskan chromium occurrences studied.
30 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

Figure 24. Water flowing from an adit of an abandoned chromium mine.
RADIOACTIVITY CONCERNS OF URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEAST- 31

RADIOACTIVITY CONCERNS OF 

URANIUM AND THORIUM DEPOSITS 

AT BOKAN MOUNTAIN, 

SOUTHEASTERN ALASKA

Naturally occurring uranium and thorium mineral

deposits are of environmental significance because they

produce radon and radium through radioactive decay. The

associated radioactivity is a health concern because excessive exposure to radioactivity can produce cancer in

humans. A few small uranium deposits are scattered

throughout Alaska, but the only uranium mine (RossAdams) is on Bokan Mountain at the south end of Prince of

Wales Island about 60 km southwest of the town of Ketchikan (fig. 25). Uranium and thorium are most widely used in

the nuclear power industry and for nuclear weapons, but

current social and political issues have depressed the prices

and demand for uranium. For these reasons, many uranium

mines, including the Ross-Adams, are presently closed, and

uranium deposits in Alaska are not currently under study.

However, because of the health concerns associated with

radioactivity, potential hazards of deposits like those on

Bokan Mountain are summarized here.

Uranium deposits on Bokan Mountain.—In 1955,

prospectors found radioactive uranium- and thorium-bearing

quartz-rich veins in granite over a 30 km2 area on Bokan

Mountain (fig. 26) (Roppel, 1991). These veins are highly

radioactive and widespread in this area, but most of the veins

are small, generally 2 cm or less in width. Primary radioactive minerals in the prospects include uraninite, thorianite,

and uranothorite. Some of the veins at Bokan Mountain

exceed 10 percent thorium ore (ThO2) and 1 percent uranium

ore (U3O8), which are considered high concentrations

(Thompson, 1988). Although several of the veins have been

prospected, only the Ross-Adams deposit has been mined

(fig. 27). Initially at Ross-Adams, a 110 m long, 15 m wide,

and 10 m deep open pit was developed (MacKevett, 1963),

but later underground workings were driven along a 110 m

long pipe. The deposit was mined intermittently from 1957

to 1971 until the ore was exhausted. Altogether, about

85,000 t of high-grade uranium ore averaging about 1 percent U3O8 was produced (Staatz, 1978). The Ross-Adams

open pit still contains some stockpiles of radioactive rock.

Human hazards of radioactive deposits.—In certain

conditions, radioactivity associated with uranium and thorium deposits can be of environmental concern. The major

health concerns for humans are long-term exposure to: 

Radon in confined air spaces. Radon concentrations

could be high near any radioactive deposit.

Uranium, radium, and radon in drinking water.

Uranium is easily oxidized by air and water, and

oxidized uranium compounds, as well as by-products

radium and radon, are soluble in water. Thorium in

water is generally of lesser concern because it occurs

in low concentrations in most surface waters, and

thorium minerals do not dissolve easily in water. 

Surface radiation and inhalation or ingestion of

radioactive dust. 

In all these cases, long-term exposure to radioactivity

must be considered unlikely because the mines on Bokan

Mountain are closed and the area is so remote. For example,

surface and ground waters near the Bokan deposits could

have high concentrations of dissolved uranium, radium, and

radon, but the area is distant from any major water supply. 

URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEASTERN ALASKA
32 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

ALASKA

Prince of Wales Island

Petersburg

Wrangell

Ketchikan

Prince Rupert

Bokan

Mountain

PRINCE OF WALES ISLAND

0 50 100 KILOMETERS

57 ̊

56 ̊

55 ̊

54 ̊

130 ̊ 134 ̊

Figure 25. Location of Bokan Mountain uranium deposits.
RADIOACTIVITY CONCERNS OF URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEAST- 33

Figure 26. View of the granitic intrusion (center) at Bokan Mountain.

Figure 27. Photograph from the 1960’s showing mining of uranium ore at the Ross-Adams mine.

URANIUM AND THORIUM DEPOSITS AT BOKAN MOUNTAIN, SOUTHEASTERN ALASKA 33
34 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA
SUMMARY 35

SUMMARY

The studies of Alaskan mineral deposits presented

herein show that various types of mineral deposits have very

different geochemical characteristics that influence the

chemistry of waters draining the mineral deposits. These

characteristics are directly related to the mineralogy,

geochemistry, and geology of each mineral deposit. For

some deposits, downstream water geochemistry may present

environmental problems for the local ecosystems. For example, the most adverse effects were observed downstream

from the massive sulfide deposits in the northwestern Brooks

Range and in Prince William Sound, where water samples

contain the highest concentrations of metals and lowest pH

values of the deposits studied here (fig. 28). Such acid- and

metal-rich waters result from the weathering of pyrite and

other base-metal sulfide minerals in these deposits that form

acid and release heavy metals during the process. Water

samples collected near the massive sulfide deposits may contain heavy metal concentrations in excess of State and Federal water standards (table 2). Although waters emanating

from these deposits are high in acid and metal content, these

waters are rapidly diluted downstream, usually within a few

kilometers below the deposits (for example, deposits in the

Brooks Range).

Most of the other Alaskan deposits studied contain low

acid and metal concentrations in water collected downstream

from the deposits (fig. 28). For example, stream waters collected downstream from mercury deposits in southwestern

Alaska have near-neutral pH values and contain low mercury

contents, suggesting that these deposits produce only minor

amounts of acid and heavy metals upon weathering. The low

dissolved mercury concentration is due to the presence of

cinnabar, which is resistant to physical and chemical weathering and does not easily form acid water. A greater environmental problem of the mercury deposits is the elevated

mercury concentrations in stream sediment samples and fish

that were collected downstream from the mines and deposits;

however, the mercury concentrations in the fish are below

the recommended FDA level for mercury in edible fish, suggesting only minor effects on local food chains. Alaskan

gold veins and gold placer deposits contain pyrite and other

sulfide minerals capable of producing acid water, but the

amount of these sulfide minerals is generally small. Thus,

weathering of such deposits does not produce water with significant concentrations of acid or heavy metals. Similarly,

the chromium-bearing deposits contain little or no pyrite,

and waters draining these deposits contain low-metal concentrations and have near-neutral pH values. 

The case studies presented herein summarize the environmental effects of several types of mineral deposits. The

results emphasize the need for additional, well-designed

geochemical studies, which are necessary for the classification and understanding of any mineral deposit, but which

will also address potential environmental concerns. Environmental geochemical studies are now a common practice in

the mining industry, before, during, and subsequent to the

mining of mineral deposits. These studies help predict

unique effects of mineral deposits on the surrounding environments. Environmental geochemistry can be useful in all

phases of mineral exploration, as well as in mine planning,

development, and remediation. 
36 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA SUM OF DISSOLVED 

0.01

Zn + Cu + Cd + Pb + Co + Ni,

IN PARTS PER MILLION

1

100

10,000

1 3 5 7 9 11

pH

high acid, high metal acid, high metal near neutral, high metal

massive sulfide deposits (northwestern Brooks Range)

ultra high acid

and metals

Au deposits

Hg deposits

Cr deposits

massive sulfide deposits (Prince William Sound)

acid, low metal near neutral, low metal

Increasing pyrite

decreasing neutralizing capacity

Figure 28. Plot of dissolved metal concentrations in water versus water pH for several Alaskan deposit types. This plot shows that the

waters emanating from Alaskan mercury, gold, and chromium deposits have near-neutral pH and low dissolved metal contents, whereas

Alaskan massive sulfide deposits form waters that are often high in acid and metal contents.

Table 2. Geochemical data summary of mineral deposits studied.

______________________________________________________________________________________

Deposit type Elements of Element concentrations in water pH range in

 environmental concern exceeding EPA-CMC standards1 stream water

______________________________________________________________________________________

Massive sulfides Pb, Zn, Cd, Cu 2,250 ppb Pb, 272,000 ppb Zn, 2.8–8.1

 (sedimentary rock 800 ppb Cd, 360 ppb Cu

 hosted)

Massive sulfides Cu, Pb, Zn, Cd 3,600 ppb Cu, 3,300 ppb Zn, 2.6–7.3

 (volcanic rock 220 ppb Pb, 27 ppb Cd

 hosted)

Gold veins As, Pb, Zn, Cd, Sb 6.4–8.0

Gold placers As, Pb, Zn, Cd, Hg 6.5–8.1

Mercury Hg, Sb, As 7.0–8.4

Chromium Cr 6.7–9.3

______________________________________________________________________________________ 1CMC is the Environmental Protection Agency’s water quality criteria to protect against acute effects in

aquatic life and is the highest instream concentration of a toxic pollutant consisting of a 1-hour average not

to be exceeded more than once every 3 years on the average.
REFERENCES CITED 37

REFERENCES CITED

For more information on the silver-lead-zinc mineral

deposits in the northwestern Brooks Range see:

Dames and Moore, 1983, Environmental baseline studies, Red Dog

Project: Prepared for Cominco Alaska, Inc., Anchorage, AK.

Kelley, K.D., 1995, Natural environmental effects of silver-leadzinc deposits in the Brooks Range, Alaska: U.S. Geological

Survey Fact Sheet 092-95. 

Kelley, K.D., and Taylor, C.D., 1996, Natural environmental effects

associated with the Drenchwater zinc-lead-silver massive sulfide deposit, west-central Brooks Range with comparisons to

the Lik and Red Dog deposits, in Moore, T.E., and Dumoulin,

J.A., eds., Geologic studies in Alaska by the U.S. Geological

Survey, 1994: U.S. Geological Survey Bulletin 2152, p. 31–46.

Runnels, D.D., Shepherd, T.A., and Angino, E.E., 1992, Metals in

water—Determining natural background concentrations in

mineralized areas: Environmental Science and Technology, v.

26, p. 2316–2323.

For more information on massive sulfide deposits in

Prince William Sound please refer to:

Goldfarb, R.J., Nelson, S.W., Taylor, C.D., d’Angelo, W.M., and

Meier, A.L., 1996, Acid-mine drainage associated with volcanogenic massive sulfide deposits, Prince William Sound, Alaska, in Moore, T.E., and Dumoulin, J.A., eds., Geologic studies

in Alaska by the U.S. Geological Survey, 1994: U.S. Geological Survey Bulletin 2152, p. 3–16.

For more information on mercury in southwestern

Alaska please refer to:

Gray, J.E., 1994, Environmental geochemistry of mercury mines in

Alaska: U.S. Geological Survey Fact Sheet 94-072.

Gray, J.E., Meier, A.L., O’Leary, R.M., Outwater, C., and Theodorakos, P.M., 1996, Environmental geochemistry of mercury deposits in southwestern Alaska—Mercury contents in

fish, stream-sediment, and stream-water samples, in Moore,

T.E., and Dumoulin, J.A., eds., Geologic studies in Alaska by

the U.S. Geological Survey, 1994: U.S. Geological Survey

Bulletin 2152, p. 17–30.

Gray, J.E., Theodorakos, P.M., Budahn, J.R., and O’Leary, R.M.,

1994, Mercury in the environment and its implications,

Kuskokwim River Region, southwestern Alaska, in Till, A.B.,

and Moore, T.E., eds., Geologic studies in Alaska by the U.S.

Geological Survey, 1993: U.S. Geological Survey Bulletin

2107, p. 3–13.

For more information on southern Alaska gold vein

deposits please refer to:

Carrick, S., and Maurer, M., 1994, Preliminary water resource

assessment of the Girdwood area, Alaska: Division of Geological and Geophysical Surveys Public-Data File 94-51, 36 p.

Cieutat, B.A., Goldfarb, R.J., Borden, J.C., McHugh, J.B., and Taylor, C.D., 1994, Environmental geochemistry of mesothermal

gold deposits, Kenai Fjords National Park, south-central Alaska, in Till, A.B., and Moore, T.E., eds., Geologic studies in

Alaska by the U.S. Geological Survey, 1993: U.S. Geological

Survey Bulletin 2107, p. 21–26.

Trainor, T.P., Fleisher, S., Wildeman, T.R., Goldfarb, R.J., and

Huber, C., 1996, Environmental geochemistry of the McKinley

Lake gold mining district, Chugach National Forest, Alaska, in

Moore, T.E., and Dumoulin, J.A., eds., Geologic studies in

Alaska by the U.S. Geological Survey, 1994: U.S. Geological

Survey Bulletin 2152, p. 47–58.

For more information on Alaskan placer deposits please

refer to:

Ray, S.R., Vohden, J., and Morgan, W., 1992, Investigation of trace

metals related to placer mining on Fairbanks and Porcupine

Creeks: Alaskan Division of Geological and Geophysical Surveys, Public-Data File 92-13, 27 p.

Swainbank, R.C., Bundtzen, T.K., Clough, A.H., Henning, M.W.,

and Hanson, E.W., 1995, Alaska’s Mineral Industry, 1994:

Division of Geological and Geophysical Surveys, Special

Report 49, 77 p.

U.S. Minerals Management Service, 1989, Mercury in the marine

environment, workshop proceedings: OCS MMS 89-0049.
38 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

For more information on chromium studies please

refer to:

Barnes, Ivan, and O’Neil, J.R., 1969, The relationship between

fluids in some fresh alpine-type ultramafics and possible modern serpentinization, western United States: Geological Society

of America Bulletin, v. 80, p. 1947–1960.

Hem, J.D., 1992, Study and interpretation of the chemical characteristics of natural water: U.S. Geological Survey WaterSupply Paper 2254, 263 p.

Simon, N.S., Demas, C., and d’Angelo, W., 1994, Geochemistry

and solid-phase association of chromium in sediment from the

Calcasieu River and estuary, Louisiana, U.S.A.: Chemical

Geology, v. 116, p. 123–135.

For more information on the mineral deposit at Bokan

Mountain please refer to:

MacKevett, E.M., Jr., 1963, Geology and ore deposits of the Bokan

Mountain uranium-thorium area, southeastern Alaska: U.S.

Geological Survey Bulletin 1154, 125 p.

Roppel, Patricia, 1991, Fortunes from the Earth—An history of the

base and industrial minerals of southeast Alaska: Manhattan,

Kans., Sunflower University Press, 139 p.

Staatz, M.H., 1978, I and L uranium and thorium vein system,

Bokan Mountain, southeastern Alaska: Economic Geology, v.

73, p. 512–523.

Thompson, T.B., 1988, Geology and uranium-thorium mineral

deposits of the Bokan Mountain Granite Complex, southeastern Alaska: Ore Geology Reviews, v. 3, p. 193–210.

For information on water standards please refer to:

Alaska Department of Environmental Conservation, 1994, Drinking water regulations: State of Alaska, Department of Environmental Conservation report 18-ACC-80, 195 p.

Environmental Protection Agency, 1992, Water quality standards;

establishment of numeric criteria for priority toxic pollutants;

States’ compliance; final rule: Federal Register, 40 CFR Part

131, v. 57, no. 246, p. 60847–60916.
GLOSSARY 39

GLOSSARY

amalgamation of gold. A process used for the separation

of gold. Gold, especially fine grained gold, can be

recovered using liquid mercury, which has the ability

to blend or stick to gold, thereby effectively extracting

gold particles from stream-sediment samples. Amalgamation of gold was widely used in the early 1900’s

for gold extraction in many gold deposits, especially

placer deposits.

acid drainage. The formation of acid water principally by

surface oxidation of rocks containing sulfide minerals,

such as pyrite (iron sulfide). When surface water

comes in contact with the sulfide minerals, sulfuric

acid is produced, which further dissolves surrounding

rocks and minerals. Metals are often more soluble in

acid solutions, and thus, acid drainage generally carries high concentrations of dissolved metals. Such

acid waters found downstream from mines are called

acid-mine drainage.

arsenopyrite. Iron-arsenic sulfide (FeAsS), steel gray to silver white in color, common in vein gold deposits and

in some massive sulfide deposits.

background concentrations. In geochemistry, this refers to

chemical concentrations in natural materials that have

not been influenced by the activities of humans. In

studies of mineral deposits, background samples are

those collected from unmineralized areas, generally

upstream from mines or distant from mineralized areas.

Thus, geochemical backgrounds represent concentrations that are considered “normal or usual” and are

unaffected by mineral deposits or mining.

bioaccumulation. Increase of metal concentrations in

organisms through uptake from water or food sources.

biomagnification. Increasing element concentrations with

ascending position in the food chain.

chalcopyrite. Copper-iron sulfide (FeCuS2), brass yellow in

color, is common in a variety of mineral deposits and is

an important ore of copper.

chromite. Iron-chromium oxide (FeCr2O4) is a hard, heavy

mineral, typically black or dark brown. Chromite is

found in mafic and ultramafic rocks and is a common

ore of chromium.

cinnabar. Mercury sulfide (HgS) is most commonly a brilliant red color. Cinnabar contains 86 percent mercury

and is an important ore of mercury.

ecosystem. An area consisting of the physical environment

and its living elements (such as plants and animals) and

nonliving elements (such as water, rocks, and soils)

that might affect this area.

galena. Lead sulfide (PbS) that commonly contains significant amounts of silver. Galena is usually silver gray to

blue gray in color, forms cubes, and is common in

many vein and massive sulfide deposits. Galena is an

important ore of lead and silver.

heavy metals. These are among the most toxic of the metals.

Copper, lead, zinc, cadmium, mercury, and iron are

common heavy metals, and such metals have high

atomic weights, and therefore are commonly called

“heavy metals.” These metals have a high affinity for

sulfur and often form sulfur compounds, and because

sulfur is easily oxidized by air and water, these metals

can be transported in water downstream from mineral

deposits that contain them. 

marcasite. An iron sulfide (FeS2) mineral, commonly light

gray to brassy in color, that has a radiating fibrous

form, is dimorphous with pyrite, and often resembles

pyrite in appearance; but marcasite has a lower specific

gravity. Marcasite is common in sedimentary rocks

and some ore deposits.
40 ENVIRONMENTAL STUDIES OF MINERAL DEPOSITS IN ALASKA

pH. A measure of the amount of acid or base in a solution,

pH is related to the concentration of the hydrogen ions.

Neutral solutions have a pH of 7, whereas the pH of

acid solutions is less than 7 and alkaline solutions have

pH values greater than 7. Acids generally have an

excess of hydrogen ions (H+) and bases have an excess

of hydroxyl ions (OH-). Sulfuric acid (H2SO4) is an

example of a strong acid, and sodium hydroxide

(NaOH), a type of lye, is a strong base.

ppb. Abbreviation for parts per billion. This is a concentration measured as micrograms per liter or as micrograms per kilogram.

ppm. Abbreviation for parts per million. This is a concentration measured as milligrams per liter or as milligrams per kilogram.

pyrite. Iron sulfide (FeS2) is one of the most widespread

sulfide minerals and is common in metallic mineral

deposits. Pyrite is typically cubic in form and palebronze or brass-yellow in color; it is often called

“fools gold.” The primary concern of pyrite in mineral deposits is its tendency to form strong acid (sulfuric acid) upon oxidation.

pyrrhotite. An iron sulfide mineral, generally bronze to redbrown in color, commonly massive and not often found

as crystals. Pyrrhotite is common in massive sulfide

deposits and may contain significant amounts of nickel;

it is therefore a source of nickel in some deposits.

sphalerite. Zinc-iron sulfide ((ZnFe)S), yellow, brown, or

black in color. Sphalerite often contains minor amounts

of cadmium, arsenic, and manganese, and is a widespread zinc ore.

stibnite. Antimony sulfide (Sb2S3), silver-gray sulfide

mineral with a bright metallic luster that commonly

forms bladed crystals containing striations. Stibnite is

the principal ore of antimony and often contains some

silver and gold.

sulfide minerals. Minerals containing the reduced form of

sulfur (S2-), which is bound with common metals, such

as iron in pyrite (FeS2), lead in galena (PbS), zinc in

sphalerite (ZnS), mercury in cinnabar (HgS), among

others. Sulfide minerals are common in many types of

metallic mineral deposits. Many of these minerals can

be of environmental concern because they can produce

acid during oxidation. When acid is formed, it can dissolve metals in surrounding minerals and rocks, releasing them into surface waters of streams and rivers.

thorianite. Thorium oxide (ThO2), a thorium ore, generally

cubic in form and highly radioactive, containing impurities or rare earth elements such as cerium.

ultramafic rock. A rock composed primarily of minerals

such as pyroxene and olivine. Ultramafic rocks are typically of igneous origin, dark in color, and consist of

peridotite, pyroxenite, and dunite rock types.

uraninite. Uranium oxide (UO2), commonly called pitchblende, is black, brown or steel gray in color, and

commonly contains thorium, radium, cerium, and

lead impurities. Uraninite is highly radioactive, easily oxidized, and common in vein mineral deposits

in granites.

uranothorite. Thorium-uranium silicate ((Th, U)SiO4),

highly radioactive, typically brown, or black, and is an

ore of uranium and thorium found most commonly in

vein deposits in granites.

Manuscript approved for publication February 28, 1996

Published in the Central Region, Denver, Colorado

Graphics by Richard P. Walker, Barbara Ramsey, and

Carol A. Quesenberry

Photocomposition and design by Carol A. Quesenberry

Edited by Lorna Carter and Carole A. Bales

Online composition by Joan G. Nadeau
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and over the counter in paperback book form.

State catalogs, “List of U.S. Geological Survey Geologic and Water-Supply Reports and Maps For (State),” may be purchased by mail and

over the counter in paperback booklet form only.

“Price and Availability List of U.S. Geological Survey Publications,” issued annually, is available free of charge in paperback booklet

form only.

Selected copies of a monthly catalog “New Publications of the

U.S. Geological Survey” is available free of charge by mail or may be obtained over the counter in paperback booklet form only. Those wishing a

free subscription to the monthly catalog “New Publications of the U.S.

Geological Survey” should write to the U.S. Geological Survey, 582 National Center, Reston, VA 22092.

Note.–Prices of Government publications listed in older catalogs,

announcements, and publications may be incorrect. Therefore, the prices

charged may differ from the prices in catalogs, announcements, and publications.